A carriage-type conveyor of this sort is disclosed in U.S. Pat. No. 4,438,701, wherein each carriage is linked to a carrier, which runs under the floor level, by means of a C-shaped coupling member which is offset in a lateral direction perpendicular to its direction of travel. Cover plates, each with a resilient strip attached to its fore end for sealing the passage of the vertical portion of the coupling member, are placed on the floor surface on which the carriage runs, thereby ensuring smooth movements of the carrier and chain while protecting them against intrusion and deposition of the paint used on the coating line or of the dust on the floor surface.
However, in the coating line, the paint deposits on the traveling wheels of the carriage, which are not provided with any dust cover. Deposited paint increases their rotational resistance or invites a problem of degradation of the coating quality by whirling paint dust since the paint on the wheels becomes loose after drying and falls everywhere in the coating line in a finely divided form.
On the other hand, Japanese Laid-Open Utility Model Application No. 60-5966 discloses a transfer system employing wheelless load support deck 1 which is free of the above-mentioned problems but unsuitable for use with coating robots due to inferior stability against sideward wavering movements.
Further, the load support deck which is supported by front and rear trolleys immovably in the vertical direction is driven by horizontal-axis wheels running on guide rails, so that a great load is imposed on the wheels and guide rails, causing considerable friction therebetween. In addition, the transfer system is held in overload condition when a foreign object gets into the gaps between the horizontal-axis wheels and guide rails, and, since the horizontal rollers are not castors, they skid sideward at curves. It is very likely that the rollers and guide rails suffer from localized abrasive wear. The above-mentioned phenomena all lend themselves to degrade the positional accuracy with respect to painting robots.
In case there is a necessity for switching the transfer of the load from continuous travel to intermittent travel for coating a work in a painting robot operating zone, for example, a continuous traveling conveyor and an intermittent traveling conveyor have to be juxtaposed at the switching point. However, it is difficult for the above-described prior art conveyors to meet this requirement due to a spatial problem.